MWCNTs impregnated with iron and copper nanoparticles by green synthesis for the removal of paraquat from aqueous solutions

Abstract

Paraquat, a widely used herbicide, is highly water-soluble, enabling its quick entry into aquatic ecosystems. In addition to being linked to Parkinson’s disease, its high toxicity causes severe damage to various organs. Multi-walled carbon nanotubes (MWCNTs) functionalized with OH were impregnated with Fe and Cu nanoparticles by green synthesis using guava leaves as reducing agents, and the resulting material was characterized and applied to remove paraquat from aqueous solutions. Adsorption studies were performed by isotherms, kinetics, and thermodynamic aspects, and the application in real river samples contaminated with paraquat. Characterization analyses confirmed that the synthesized adsorbents retained their structural integrity (XRD) and surface morphology (SEM). FTIR analysis validated the green synthesis and metal impregnation. Both materials were classified as mesoporous, exhibiting a specific surface area greater than 90 m² g⁻¹. The adsorbents efficiently removed more than 80 % of paraquat in a pH range from 4.0 to 8.0. However, the adsorption decreased at pH higher than 8.0. Besides, fast kinetic processes were found, reaching the equilibrium within 10 min. In addition, the Brouers-Sotolongo model represented the equilibrium curves, with the maximum adsorption capacity from 7.9 to 8.2 mg/g at pH 7, under a temperature of 328 K and an initial paraquat concentration (C₀) of 10 mg/L. Thermodynamics revealed na endothermic and physical adsorption phenomenon. The novel adsorbents also efficiently treated real river samples, removing around 78 % of paraquat. MWCNTs impregnated with Fe and Cu nanoparticles are interesting candidates for treating waters containing paraquat.